When you're working with a More Info page which is not updating, or doesn't exist at all, there are a few different reasons that may cause this. We'll detail them below and show how to resolve each one:
1. More Info Page Checkbox
Under Edit Product Info for a product, check the "More Info Page" checkbox in the "More Info Pages" section to make sure the checkbox is turned on.
2. Unassigned Product
Also under Edit Product Info for a product, check the "Assign Product to Pages" option to make sure the product is assigned to at least one page. If it is not assigned the More Info page will not be created. If you are testing and don't want to assign the product to a page where customers may see it, you could add a new page to your site and assign the product to it. The page it's assigned to doesn't have to be linked anywhere on your site and is only needed to cause the More Info page to be generated.
3. No Support In Product Template
Determine which template is assigned to your product with the "Template" field under Edit Product Layout and check the template to make sure it has a "[-- DEFINE MORE_INFO_PAGE --]" section. That section of the product template is used to create the More Info page and if it is missing the page will not be created.
4. Non-Supporting Template Hardcoded Into Products Loop
For the page that your product is assigned to, check the page template for the Loop Products code, which will look similar to this:
[-- LOOP PRODUCTS --]
[-- PRODUCT --]
[-- END_LOOP PRODUCTS --]
If the [-- PRODUCT --] tag has a template hard-coded into it, that will override the template that you reviewed under #3 above. A tag with a hard-coded template looks like: [-- PRODUCT Template_Name --], which would appear like this in the template:
[-- LOOP PRODUCTS --]
[-- PRODUCT Template_Name --]
[-- END_LOOP PRODUCTS --]
In this example, the "Template_Name" template is overriding the product template, so you would need to check the "Template_Name" template to make sure it has a "[-- DEFINE MORE_INFO_PAGE --]" section, just like you did above for item #3.
5. Subproduct Using Non-Supporting Parent Template
Similar to #4 where a template can be overridden with the [-- PRODUCT --] tag, a Subproduct can use it's own template instead of the one assigned to it's parent product.
To see if this may be the case for your site, review the "Use subproduct's template for More Info Pages" field under Utilities > Publish. If that field is unchecked then your parent product's template will be used for it's subproducts. If the field is checked then a subproduct's template will be used during publishing and you would then want to check the subproduct's assigned template to make sure it supports a More Info page.
6. Product Assigned To Multiple Pages
When a product is assigned to multiple pages, the first page that is published during a full regeneration or a partial publish is used to create a product's more info page. Therefore, if you know the assigned product template is fine, and the page you recently assigned your product to has a valid template, but the More Info page is still not updating correctly - review all pages that you have your product assigned to. One of them may me hard-coding a template (see #4 above) that doesn't support a More Info page. Pages are not necessarily published in alphabetical or numerical order, so be sure to review all the pages you have your product assigned to since any one of them could be published first.
7. More Info Section Dependent On A Variable
If you've checked all of your templates and everything looks fine but the More Info page is still not correct, your product template may be using a variable to determine which template is used for the More Info page. In your product template, check the [-- DEFINE MORE_INFO_PAGE --] section for code similar to this:
[-- IF VAR.MoreInfoTemplate --]
[-- INCLUDE VAR.MoreInfoTemplate PROCESS --]
[-- ELSE --]
[-- INCLUDE Classic-MoreInfoPage PROCESS --]
[-- END_IF --]
In this example a variable called "MoreInfoTemplate" is checked and if it is set then the variable value is used as the filename for the more info template, otherwise the "Classic-MoreInfoPage" template is used. If you see code like this in your template, then even though you've updated a More Info template, a different one may be used. You can review your templates, especially the [-- DEFINE PAGE --] section of the page template for the page your product is assigned to, to determine that value of the variable and see which exact template is being used to create your More Info Page.
One thing to remember is variables persist as pages and products are published, so a variable could be set for a specific page or a specific product and then be used later with a different value then intended. This is more likely to be a problem if you have a product assigned to different pages with different templates (see #6 above). If your More Info page is still not generated as expected, be sure to review all pages your product is assigned to, along with any variables that are used to set a More Info template filename.